why cant i find the right average Nusselt number?
 

Hi friends:),
i am simulating natural convection in square cavity: i computed the Nu average by fluent 6.3 : facet average/wall fluxes/surface nusselt number/heat wall
but my results is bigger than the results benchmark(de Vahl Davis)
have i a mistakes:confused:?please explain me how to get best results ,could u give me all the steps please?
thank you very much